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The anomalous positive magnetoresistance (PMR) in Co(sub x)-C(sub 1-x) granular films prepared on silicon(100) substrates by pulsed laser deposition method is reported. A larger positive MR is observed at room temperature that at low temperature.

A large positive magnetoresistance (MR) has been found in micro-sized Fex–C1−x composites. At a magnetic field of 5 T, the Fe0.2–C0.8 composite has the largest MR, 53.8% and 190% at room temperature and at 5 K, respectively. The magnetic field dependence of the MR can be described approximately as MR∝Bn, and the value of exponent n is determined by the Fe weight concentration and temperature, ranging from 1/4 to 6/4. It appears that Fex–C1−x has a linear field dependence of the positive MR at different temperatures. The possible mechanism for the positive MR is discussed. [Copyright &y& Elsevier]

Positive magnetoresistance (MR) has been found in Cox–C1−x composites (x=10, 20, 30 and 60 wt%) with an average particle size of 23.5 μm. The composite shows a linear field dependence of the MR at higher magnetic fields (3 T<B<8 T) with no saturation of the MR even at B=8 T at room temperature. Among the Cox–C1−x composites, Co10–C90 has the largest MR value of 58.9% at room temperature with B=8 T and the MR value of 105.6% at a temperature of 5 K with B=5 T. The possible mechanism for the positive MR is discussed. [Copyright &y& Elsevier]